Manufacture of paper pulp



Patented Aug. 4, 1936 MANUFACTURE OF PAPER PULP Louis Leonard Larson, Hockessin, and George Lewis Schwartz, Wilmington, Del., assignors to E. I. du Pont de Nemours & Company, Wilmington, Del., a corporation of Delaware No Drawing. Application June 5, 1934,

Serial No. 729.154

Claims. (01. 92-9).

This invention relates to the manufacture of pulp from raw cellulosic material, and more particularly to an improved method of making p p pulp from wood chips. I

4 In the pulping of wood by either alkaline or acid procedures, it has long been recognized that the rate of penetration of the wood by cooking liquor is an important factor in determining the choice of operating" conditions, and also is influential in determining the quality of the pulp produced. It is also generally agreed that rapid penetration of pulping liquor into the wood increases the rate of pulping under any given set of conditions and improves generally the quality 15 of the final product. It is natural, therefore, that numerous methods have been suggested to take care of this problem of liquor penetration. Among the common methods now in use for achieving this purpose are, the custom of cutting 20 wood into small chips prior to digestion and insuring that the size of these chips be reasonably uniform in order that they maybe penetrated at a uniform rate. Another fairly common practice in the industry is to add pulping liquor or 25 partially exhausted liquor to the chips and allow the latter to soak for some time, in some cases up to 24 hours have been used, in order to insure uniform penetration of the cooking liquor into the wood before starting the actual pulping proc- 30 ess. Sometimes the initially added penetrating liquor is removed (drained from the chips) and other fresh liquor added for the main digestion process. Such procedures have the disadvantage, however, of. consuming considerable time and 35 holding up digester capacity.

Other methods, which have either been proposed or used in the past as means for increasing the rate of penetration of a cooking liquor into wood chips, have consisted in steaming the chips prior to adding the cooking liquor, or in the use ofhigh pressures in the digesters during the first stages of the regular digestion process. In the case of acid cooking (sulflte process) higher pres- 45 sures have been secured by using liquors containing excessive amounts of free sulfur dioxide, but

the preparation of such acidsis usually diflicult to achieve and is wasteful of this valuable pulping constituent. For alkaline digestions v(soda or 50 sulfate processes) high pressures near the start of the digestion have been secured by use of preheated liquors and vigorous injection of live steam into the digester or, as outlined in one patented process, by'making use of an inert gas 5 such as nitrogen, which is injected into the dig ter under high pressure. Still another patented method for increasing rate of penetration at be. ginning of digestion is to subject the wood to a vacuum treatment or to treatment under high pressure with a water soluble gas such as am- 5 mom'a, in order that air entrapped in the chips may be removed prior to adding the cooking liquor.

This invention has as an object an impr oved method for making pulp. A further object is an improvement in pulp manufacture which produces greater operating economy and eificiency in operation through rapid penetration of the digesting liquors into the raw cellulosic material without recourse to the prior art methods mentioned above.

The foregoing objects of this invention are accomplished by addition to the digestion liquor (either acid or alkaline in nature) of wetting out agents which greatly assist in the penetrationof the active pulping agents into the wood or other cellulosic material.

The agents useful in the practice of our invention include those substances, such as organic sulfonates and sulfates, which are known to increase the wetting properties of liquids. The present process may be carried out with compounds or mixture of compounds of an organic nature which cause marked reduction in interfacial tension between .wood and a digestion liquor composed of either acid, base or mixtures of acids or bases with either netural, basic or acid salts.

The concentration of the wetting agent, which in the present invention functions as anagent for causing penetration of the cooking liquor into the wood, will depend to some extent on the agent selected and on other operating conditions used in the cooking process. With these considerations in mind, the range of concentrations useful in the carrying out of this invention may be placed between 0.001% and 1% of the weight of the cooking liquor used. ,With most of the agents .cause external heating was used instead of direct heating by steam injection.

Example 1 Using an externally heated dead lined digester, two parts of air dried spruce wood chips are just covered with ten parts of a sulfite cooking liquor made up with a calcium base and containing approximately 1% combined S02 and 3.2% free $02. To this liquor is also added 0.1% based on the weight of the cooking liquor of sulfate of normal dodecyl alcohol. The digester is closed and heated to approximately 110 C. in approximately two hourstime, then gradually the temperature is raised during 1.5 hours to 140 C. and held there until the fiber is completely liber- 15 ated, which requires about 6 hours. The heat is then removed, the digester blown, and the product washed with water. The unbleached pulp is screened in order to separate out shives (undigested portions of wood) and the screened pulp 20 bleached with calcium hypochlorite solution. Yields of unbleached pulp' obtained under these conditions are higher (generally 23-10%) and the proportion of shives lower, (sometimes more than 50%), than are obtained from the same wood digested under comparable conditions except for the presence of the wetting agent. Furthermore, the screened pulp produced with the aid of the wetting out agent can be bleached to a satisfactory white color using -25% less bleach than 30 is possible in the absence of such agents.

' other indication of the beneficial influence of the wetting agents in the above experiment is a complete absence of any tendency for the pulp produced in the presence of the wetting agent to 35 burn or darken, although this condition is encountered in the absence of such agents under the other pulping conditions outlined above, due

probably to the rapidity with which the temperature is raised during the early part of the digestion.

. 9 Example II An alkylated naphthalene sulfonic acid is substituted for sulfate of normal dodecyl alcohol in an experiment otherwise conducted in exactly the 45 same manner as under Example I. Under these conditions and with this wetting agent results obtained on .time of digestion, yield, andimprovement of the pulp, with respect to screenings and bleachability, are substantially the same as.those 50 obtained under Example I using the sulfate of dodecyl alcohol.

Example III so and held at this temperature until the fibers are completely liberated. The digester is then blown and the pulp worked up under conditions similar to those used in Examples I and II. The time of digestion used in this experiment is slightly 65 under that producing best results in the absence of a wetting out agent as is indicated by the fact that yields of screened pulp (free of shives) are approximately 23-20% greater and the proportion of shives correspondingly lower than is obtained from a comparable experiment made without the aid of a wetting agent. Bleach requirements forsoda pulp digested in the presence of sulfate of normal dodecyl alcohol are 75 found to be lower (in most cases 10-20%) than is the case with pulp similarly digested except for the presence of the wetting agent.

Example IV Using the same digestion equipment as in Ex- 5 ample III, a kraft or sulfate type liquor is prepared containing grams per liter NaOH and 10 gramaper liter of NazS. Ten parts of this liquor is run into the digester with two parts of jack pine chips and 0.05% of cresylic acid based on 10 the weight of the cooking liquor. The digester is heated to 120 in one hour and held at this temperature until digestion is completed after about three hours, and is then emptied. The resulting product is obtained in a well pulped 15 condition, is fairly light in color, and can be bleached to a good white color. In comparison,

.not be used in acid liquors and they are not satisfactory agents in alkaline cooking liquor for increasing the rate of penetration of the liquor into the wood, chiefly because ordinary soaps tend to deposit insoluble calcium and magnesium salts in the pulp.

Examples of agents useful for increasing the rate of penetration of acid pulping liquors (sulfite process) into the interior of the chips are the sulfonates and sulfates of carbocyclic and alkyl substituted carbocyclic compounds containing less than 5 carbon atoms in the alkyl substituent. Examples of these compounds are as follows: (1) 4o alkylated naphthalene 'sulfonicacids including methyl, ethyl, isopropyl, and isobutyl derivatives (mono-, diand trisubstituted), (2) sulfonated tetralin, (3) sulfonated abietene, (4.)v sulfonated abietane, (5) sulfonated condensation products of abietene or abietane with epichlorhydrin (as sodium salts), (6 sulfated and sulfonated normal, primary aliphatic alcohols, saturated or unsaturated, and including ricinoleyl and linoleyl alcohols, (7) sulfonated oleflnes such as sulfodecene, (8) condensation products of oleic acid or oleyl acid chloride with ethionic acid or taurine.

There 'exists a wider choice of penetrating agents which may be used to advantage in alkaline pulping liquors (soda or sulfate processes) which include, in addition to fatty alcohol 8111- fates and all other compounds on the foregoing acid list, materials such as cresylic acid and various coal tar derivatives such as phenols, xylenols, etc. Among the latter group may also'be included substituted phenols of thetype of chlorinated phenols, etc. Furthermore, the foregoing materials may be used either singly or in combination with one another.

The advantages secured by the use of a wetting out agent in a process producing pulp from wood are many and ,varied, depending on the type of wood and process used, but some of the more important of these are: (1) penetration of the cooking liquor, whether acid or alkaline, is accelerated, thus reducing the total time required for pulping, (2) in, the case of acid cooking (sulfite process) the rapid penetration of the liquor into the chips'which accompanies the use of a wetting out agent minimizes the danger of'75 buming or injury to the cellulose by too rapidly raising the temperature at the start of the cooking process, (3) the rapid penetration of cooking liquor into chips which accompanies the use of a wetting agent increases the uniformity of the pulping process and therefore the uniformity,

of the product, ,so that percentages of shives (bundles of incompletely liberated fibers) and fines (over-digested fibers commonly originating from the outside of the chips) are minimized, (4) under comparable operating conditions of cooking liquor composition, temperature, pressure, and time of digestion, pulp produced in the presence of a wetting agent is obtained in higher yields, is easier to bleach, and is of better color in the bleached condition than is pulp processed without the aid of any such agent, (5) another advantage following the use of these agents as compared to materials such as soaps, etc. which might be used is the complete freedom from precipitation of insoluble salts of calcium and magnesium in the liberated fibers.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appendedclaims.

We claim:

1. A' process for manufacturing paper pulp from wood chips which comprises cooking wood chips in a pulping liquor of the class consisting pulp.

of sulflte, soda, and kraft pulping liquor which contains a small amount of an agent selected from the class consisting of sulfonates of carbocyclic and alkyl substituted carbocyclic compounds containing less than 5 carbon atoms in 5 the alkyl substituent, said agent being unaffected chemically with retention of its wetting properties during the heat treatment required for the conversion of the wood chips into paper 2. A process for manufacturing paper pulp from wood chips which comprises cooking wood chips in a pulping liquor of the, class consisting of sulflte, soda, andkraft pulping liquor, said liquor containing from 0.001% to 1% of a compound which is a wetting agent and which is unaffected chemically with retention of its wetting properties during the heat treatment required for the conversion of the wood chips into p p pu p- 2o 3. The process set forth in claim 1 in which the sulfonate is an alkylated naphthalene sulfonate.

4. A process for manufacturing paper pulp from wood chips which comprises cooking wood chips in an alkaline pulping liquor containing from 0.001% to 1% of a higher-alcohol sulfate.

5. The process set forth in claim 2 in which the wetting agent is one of the class consisting of organic sulfonates and sulfates.

LOUIS L. LARSON. GEORGE LEWIS SCHWARTZ. 

